When a blend or mixture is prepared from two or more ordinary, non-polymeric materials, a random distribution of the molecules of the components is obtained. This random distribution provides complete mixing without the formation of groups or clusters of the molecules of any one component. Such a mixture is expected to follow the "Rule of Mixtures." The Rule of Mixtures predicts the numerical values of properties, such as tensile and flexural strengths and tensile and flexural moduli, of a blend to be the weighted average of the numerical values of the properties of the components. A discussion of the Rule of Mixtures can be found in the book Predicting the Properties of Mixtures: Mixture Rules in Science and Engineering, by Lawrence E. Nielsen, Marcel Dekker, Inc. (New York: 1974).
Further information with regard to the Rule of Mixtures can be found on pages 395, 436, 465, 492, and 500 of Volume 2 of Mechanical Properties of Polymers and Composites, by Lawrence E. Neilsen, Marcel Dekker, Inc. (New York: 1974). As stated therein, mixtures of a polymer matrix with a fibrous reinforcing agent, a ribbon-shaped filler, or a rod-shaped filler are known to often follow the Rule of Mixtures. The above-cited referehce further discloses that mixtures of phase inverted isotropic interpenetrating polymer networks, such as a phase inverted network of polystyrene and polybutadiene, are also known to follow the Rule of Mixtures.
Mixtures of most chemically distinct polymeric materials have been found to deviate from the behavior of ordinary mixtures as characterized by the Rule of Mixtures. The sheer size of polymeric chains restricts mixing of the components and leads to the formation of domains or clusters of molecules of the individual components. Thus, it can be said that most chemically distinct polymeric materials tend to be incompatible in mixtures and exhibit a tendency to separate into phases. There often exists a boundary between the domains of the component polymers, and articles made from such a blend would be expected to exhibit failure at the boundary when placed under stress. In general, then, the mechanical properties of the product are commonly reduced rather than enhanced. Specific properties which may be thus affected include tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength.
Some polymeric materials exhibit an ordered structure in at least some regions of the polymer. This order can exist in one, two, or three dimensions. The inclusion in blends of polymeric materials exhibiting an ordered structure leads to an increased tendency of the blends to separate into phases. This is due to the fact that the order found in certain regions of the polymer causes a fairly sharp boundary between the domains of the molecules of the component polymers. Thus, blends including such polymers could be expected to exhibit a significant reduction in mechanical properties. Accordingly, there has been little impetus to form such blends, particularly for use in applications where mechanical properties are of importance.
Representative disclosures of polymer blends which may include at least one polymeric component that is capable of forming an ordered or anisotropic structure in the melt phase are found in U.S. Pat. Nos. 4,228,218; 4,267,289; 4,276,397; 4,386,174; 4,408,022; 4,451,611; 4,460,735; and 4,460,736; European patent application No. 0041327; and in commonly assigned U.S. Ser. Nos. 158,547, filed June 11, 1980, now U.S. Pat. No. 4,489,190, and 461,886, filed Jan. 28, 1983. In U.S. Pat. No. 4,386,174 at Col. 4, lines 47 to 49, poly(esteramides) capable of forming an anisotropic melt phase are identified in passing as being anisotropic melt-forming polymers which can be used to render another polymer melt-processable. Also, commonly assigned U.S. Pat. No. 4,267,289 contemplates forming a polymer blend from a pair of specifically defined wholly aromatic polyesters which are each melt-processable in the absence of the other and are each capable of forming an anisotropic melt phase.
It is an object of the present invention to provide an improved melt-processable polymer blend which is capable of forming a anisotropic melt phase.
It is an object of the present invention to provide an improved polymer blend wherein a synergism has been found to exist between the polymer blend components which leads to an ability to form shaped articles from the same that exhibit surprisingly outstanding mechanical properties
It is an object of the present invention to provide an improved polymer blend which can be used to advantage to form improved molded articles, improved melt-extruded three-dimensional articles, etc.
It is an object of the present invention to provide an improved polymer blend which following injection-molding is capable of exhibiting at least one mechanical property (e.g., tensile strength, tensile modulus, flexural strength, or flexural modulus) which exceeds that of each of the polymeric components of the blend when separately injection-molded.
It is another object of the present invention to provide an improved polymer blend which is morphologically homogeneous and which has been found to possess a rheology amenable to the formation of improved shaped articles (e.g., a blend melt viscosity which is lower than that of each of the polymeric blend components).
It is a further object of the present invention to provide improved shaped articles such as improved injection-molded articles, improved melt-extruded three-dimensional articles, etc., formed from the polymer blend of the present invention.
These and other objects, as well as the scope, nature and utilization of the claimed invention, will be apparent to those skilled in the art from the following detailed description and appended claims: